Resistor



M. J. BRAUN RESISTOR May 26, 1964 2 Sheets-Sheet 1 Filed May 24, 1963 INVENTO MM W FIG. I.

Iva/ 4 ATTORNEY y 1964 M. J. BRAUN 3,134,954

RESISTOR Filed May 24, 1963 2 Sheets-Sheet 2 FIG. I3. FIG. I4. FIG. I5. FIG 16,

FIG. 17.

mvENToR:

United States Patent I This invention relates to resistors that are used for conducting high-potential current in a" distributor for the ignition system of an internal combustion engine.

One object of the invention is to provide an ignition distributor with an improved resistor for conducting current from the main power lead of the distributor to the rotor which successively contacts with the conductor segments for individual spark plug leads of the distributor.

It is another object of the invention to provide an improved resistor for use in ignition system distributors and with a conductor spring molded into one end of the resistor so as to obtain a unitary assembly which provides reliable conducting of current and which reduces the time and cost of the distributor assembly.

Another object of the invention is to provide improved methods for making resistors for use in ignition distributors, and more especially for making the improved resistor of this invention.

The invention includes a carbonaceous brush having a main body portion on which is molded an end of bonding graphite which is hard and which has good contact and good brushwear qualities for contact with the distributor rotor. The resistor of this invention also has a conducting spring with one end imbedded in an end of the resistor made of bonding graphite which forms an integral part of the resistor.

The method aspects of the invention provide steps by which such a resistor can be manufactured economically and by a process which subjects the graphite to high pressure without producing any permanent set in the coils of the attached spring.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds. In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views: 7

FIGURE 1 is a view, partly in section, showing a distributor equipped with a resistor made in accordance with this invention;

FIGURE 2 is an exploded, isometric view showing a spring and washer which are used for one of the embodiments of the invention;

FIGURE 3 is a sectional view showing the way in which the spring and washer of FIGURE 2 are assembled with one another in the first step of the process of this invention;

FIGURES 4-9 are diagrammatic sectional views showing other successive steps in the manufacture of a resistor made in accordance with this invention;

FIGURE is an elevation showing the completed resistor made by the steps of FIGURES 3-9;

FIGURE 11 is a diagrammatic sectional view showing a method for making another modified form;

FIGURE 12 is an elevation of the modified form made by the process of FIGURE 11;

FIGURE 13 is a sectional view through another form of the invention;

FIGURE 14 and 15 are sectional views showing another modified form of the process of this invention;

FIGURE 16 shows a modified form of resistor made according to the process illustrated in FIGURES 14 and 15; and

Patented May 26, 1964 FIGURE 17 is an enlarged end view of the spring shown in FIGURE 16.

FIGURE 1 shows a distributor 10 for an ignition system. This distributor has a cap 12. An ignition cable 16 is'connected with each of the bosses 14, and each ignition cable 16 connects with a fixed conductor 18 within the cap 12.

The distributor has a rotor 20 which is driven in timed relation with the crank shaft of the engine in accordance with conventional practice. This rotor includes a conductor 22 one end of which constitutes a movable contact 24. As the rotor 20 turns, the movable contact 24 successively passes in operative relation to the individual fixed contacts 18 of the diiferent ignition cables 16 to supply power to the different spark plugs of an engine in accordance with the intended firing order. There is a brush or resistor 26 in contact with the conductor 22 at the axis of rotation of the rotor 20.

Within the distributor cap 12 there is a metal insert 30 with a backing 31 having a threaded socket for receiving a complementary fitting 32. The complementary fitting 32 is secured to the conductor of a main highpotential lead 34 which enters the cap 12 through an insulating bushing 36.

At the lower end of the metal insert 30 there is a socket 40 for holding the resistor 26. This resistor 26 slides up and down in the socket 40 and is urged downwardly into contact with the conductor 22 by a spring 44. The socket 40 tapers to a smaller diameter toward its upper end and the upper convolution of the spring 44 is of large enough diameter to wedge into the tapered upper end of the socket 40 to retain the spring 44 in the socket. This wedging fit prevents the resistor 26 from falling out, when the cap 12 is removed from the distributor, because the spring 44 is embedded in the upper end of the resistor 26, in a manner which will be described. Current from the lead 34 is supplied to the resistor 26 through the spring 44, which is preferably made of beryllium copper or other spring material having good electricity-conducting properties.

In the construction illustrated in FIGURE 1, there is a metal washer 43 held against the upper end of the resistor 26 by the first coil of the spring 44. FIGURES 2 and 3 show the way in which the spring 44 is assembled With the washer 48 as the initial step in the manufacture of the resistor. The washer 48, which is preferably a metal stamping, has a center hole 50 with a diameter substantially equal to, but just a little less, than the diameter of the wire of which the spring 44 is made.

FIGURE 3 shows a straight end portion 52, of the spring 44, inserted through the opening 50 of the washer 48. This end portion of the spring fits through the opening 50 with a force fit and the end portion 52 is pushed into the washer until the first convolution of the spring 44 strikes against the washer to prevent further relative. movement.

The end portion 52 is preferably straight and co-axial with the longitudinal axis of the spring 44. In the illustrated construction, the spring 44 is a helix and this is preferable to a spring with successively smaller convolutions since it facilitates the manufacture of the resistor and assists in guiding it. A substantially flat end convolution 54 is provided at the end of the spring 44 remote from the washer 48 for contact with the upper end of the socket 40.

FIGURE 4 shows the next step in the manufacture of the resistor. The spring 44, with the Washer 48 attached,

is inserted into a cylindrical die cavity 60 in a die 61 and is'allowed to drop down in the cavity until the end portion 52 of the spring comes in contact with a plunger 62 which moves within the die cavity 60 as a piston.

The spring 44 is held with the axis of its helix substantially coincident with the axis of the cylindrical die cavity 60 while sand 66, or other filler material, is placed in the die cavity 60. This sand fills up the space in the die cavity above the washer 48, and it is desirable that the washer 48 should fit the die cavity 60 as a piston so as to prevent the leakage of sand past the washer 48. When the sand 66 reaches the upper end of the spring 44, as shown in FIGURE 5, another plunger 67 is inserted into the die cavity, and the die 61 is then turned upside down.

FIGURE 6 shows the die 61 after it has been inverted,

and after the plunger 62 has been removed. This leaves the end portion 52 of the spring 44 projecting upwardly into an open portion of the die cavity 60. The next step in the process is the insertion of graphite into this open portion of the die cavity 60. A quantity of graphite powder 68 is first inserted in the die cavity on top of the washer 48 and preferably for a depth somewhat greater than the extent of the end portion 52 of the spring above the washer 48. This graphite powder is of a composition for making a hard, wear-resistant brush. 7 On top of the powder 68, a quantity of composition carbon powder mass 70 (FIGURE 8) is inserted into the die cavity 60. This mass 70 is of a composition to supply a conductivity path for suppressing sparking noise which would interfere with good radio reception.

FIGURE 8 also shows a quantity of a graphite powder 72 which is placed on top of the carbon powder mass 70 to provide a hard upper end for the resistor. The plunger 62 is then brought back into the die cavity 60 and the plungers 62 and 67 are pressed together with substantial force, as shown in FIGURE 9, to compress the graphite 68 and 72, and the carbon powder mass 70 which is located between the quantities of graphite. The spring 44 is not affected by this compression of the graphite and carbon powder mass because the sand 66, or other filler material, transmits pressure between the washer 48 and the plunger 67 without compressing the spring.

The graphite and carbon powder compress into a permanent, unitary body under the pressure in the manner conventional for the manufacture of carbon brushes. The lower plunger 67 is then removed and the sand 66, or other loose filler material, falls out of the die cavity, leaving the spring 44 free of any coating. The resistor, consisting of the spring 44, washer 48, and end portion 52, molded into an integral mass of resistor material 68, 70 and 72, is pushed out of the die cavity 60 by the upper plunger 62. 7

FIGURE 10 shows the completed resistor 26 after it is ejected from the die cavity. The sides of the reseistor are smooth and so is the end portion which is remote from the spring 44. The resistor 26, will, therefore, move up and down freely in the distributor socket when necessary and the end of the resistor 26, which contacts with the distributor rotor, has low friction and is highly resistant to wear.

FIGURE 11 shows a method of making a modified form of the invention. In place of the spring 44, a somea what diflerent form of spring 78 is used. This spring 78 differs from the spring 44 only in that it is the same at both ends, there being a fiat convolution 54' at each end of the spring. The spring is inserted in the die cavity 60 with sand or other filler material 66, in the same way as already described. The amount of sand used is limited so that after settling, there are several coils of the spring 78 extending above the sand.

The space within the die cavity 60 is filled with graphite and composition carbon powder mass in the same way as previously described, the quantities of graphite and carbon powder being indicated by the same reference characters as in FIGURES 8 and 9 but with a prime appended. The upper coils of the spring 78 are molded in situ into the hard graphite 68 and the final resistor 80, shown in FIG- URE 12, has most of the convolutions of the spring 78 free and only a few dead coils molded on block during the compression and heating of the graphite and carbon powder.

FIGURE 13 shows a modified form of the resistor which is the same as that made by the method illustrated in FIGURES 3-9 except that a quantity of powdered copper is used at the upper end of the resistor in place of the graphite 68 used in FIGURE 8. The copper powder 85 packs into a rigid mass integral with the copper washer 48 and the carbon powder mass 70.

This construction shown in FIGURE 13 has the advantage, as does the construction shown in FIGURES 310, that the spring 44 is held in the resistor by the end portion 52 and thus the convolutions of the spring 44 can have substantially the same diameter as the body of the resistor.

FIGURE 14 shows a method of making a resistor which is similar to those shown in the other figures except that it has a different kind of spring. In FIGURE 14 the spring 88 is constructed with convolutions that are of progressively larger diameter toward the free end of the spring. In an end view, as shown in FIGURE 17, the convolutions of the spring form a spiral.

In the method illustrated in FIGURE 14, no sand is placed in the die cavity between the washer 48 and the lower plunger 67 The spring 88 is made flexible enough so that it can be compressed to the limit, with all of the convolutions lying in a spiral in a single plane, without causing any permanent set to the spring 88.

FIGURE 15 shows the graphite 68 and 72 under pressure with the carbon powder mix 70 between them and with the spring 88 compressed to the limit between the washer 48 and the lower plunger 67. Following compression, the plungers 62 and 67 move apart and the spring 88 expands to its original length. The product is ejected from the die cavity and the final resistor has the appearance shown in FIGURE 16. With this construction, an end convolution 90 of the spring 88 has substantially the same diameter as the body portion of the resistor and this serves to hold the spring and resistor straight in a cylindrical guide. The method shown in FIGURES 14 and 15, however, does not allow the same choices of spring flexibility and wire size since it is limited to a spring which can be compressed, as illustrated, without damage or permanent change in the unstressed length of the spring and without damage to the connection of the washer 48 with the end portion of the spring.

The final resistor made by the method shown in FIG- URES 14 and 15 is designated in FIGURE 16 by the reference character 95. The graphite end formed by compacting of the graphite 72 is designated by reference character 72'. Similarly, the portions of the resistor formed by compacting the carbon powder mix 70 and the graphite 68 are indicated by the reference characters 70' and 68', respectively.

The graphite portions 68 and 72' have good conductivity and excellent wearing qualities. By way of illustration, the mixes 68 and 72 used for the graphite ends in this and the other forms of the invention disclosed are composed of suitable proportions of graphite and resin binder, which are suitably blended and then passed through a 35 mesh screen. It will be understood that other mixes can be used.

The portion 70, and the corresponding portion of each of the other forms of the invention disclosed, which portions are formed by compacting the carbon powder mix 70, have substantially higher resistance for the purpose of suppressing radio interference. A common practice in making resistors for a predetermined resistance is to use two different mixes, one of which has more than the desired resistance and the other of which has less. The two mixtures are blended together to control the resistance.

For example in preparing a mix for a resistor of 10,000 ohm resistance, a mix of 8000 ohms may be blended with one of 14,000 ohms in the proportions necessary to obtain 10,000 ohms. By way of illustration, suitable parts of a base mix and pitch are mixed with a portion of carbon black, depending upon the desired resistance, and the mix is then passed through a 35 mesh screen.

The base mix in the above example can be made of suitable parts of sand, one or more grades of resin in mixture, and acetone; the mix is preferably but not necessarily screened through a 45 mesh screen.

The preferred resistors and methods of making them have been illustrated and described, and illustrative materials for the resistors have been included, but it will be understood that changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

What is claimed is:

1. In an ignition system of the type wherein a dis tributor has a rotor with a contact extending from a center portion of the rotor to a movable contact that is moved by the rotor across a plurality of fixed and angularly spaced contacts connected with conductors extending to the spark plugs of the iginition system, and in which power is applied to the rotor through a main high potential lead above a center region of the rotor, the combination with said rotor of a metal holder connected with the high potential lead and having a socket therein immediately above the rotor, a brush that fits into the socket as a guide and that is longitudinally movable in the socket, the brush having an end portion of hard graphite extending from the socket into contact with the contact on the rotor, a spring imbedded in the end of the brush and compressed between the inner end of the brush and the end of the socket, the brush having a body portion, between the spring and the hard graphite end portion, made of a compressed composition carbon powder mix that provides a controlled conductivity path for suppressing sparking noise that interferes with radio reception.

2. The ignition system described in claim 1 characterized by the spring having the diameter of its helical convolutions, when uncompressed, smaller than the diameter of the socket and smaller than the diameter of the brush.

3. The combination, in an ignition system for spark plugs, of a rotor for successively supplying power to different conductors leading to the respective spark plugs, a main power supply conductor, and a brush completing a circuit between the main power supply conductor and the rotor, said brush having an end portion of hard graphite in contact with the rotor and serving as a wearresistant bearing surface between the brush and the rotor, a body portion of the brush being of one piece construction with the end portion and made of a compressed composition carbon powder mix that provides a controlled conductivity path for suppressing sparking noise that interferes with radio reception, and a spring imbedded in the end of the brush remote from the rotor and about which the brush is formed as a one piece carbonaceous mass, said spring being in position to hold the brush against the rotor.

4. A resistor for use as a brush in a distributor of an iginition system, said resistor having an end portion made of hard compressed graphite for contact with a moving part of a distributor, a body portion of the resistor made of compressed carbon powder with a binder, and a helical spring having an end portion imbedded in the end of the resistor remote from the compressed graphite end, the resistor being formed about the imbedded portion of the spring and of one piece construction with the graphite end portion.

5. The resistor described in claim 4 characterized by the resistor having a hard graphite end portion in which the spring is embedded, and the body portion of the resistor betweene the graphite end portions being of softer carbonaceous construction.

6. The resistor described in claim 5 characterized by the resistor being of uniform cylindrical cross-section throughout its length and having a smooth cylindrical outside surface.

7. The resistor described in claim 4 characterized by the spring having a straight end portion substantially coincident with the longitudinal axis of the spring, and this straight end portion being the part of the spring that is imbedded in the resistor.

8. The resistor described in claim 7 characterized by,

a washer of substantially the same diameter as the resistor and with an opening thereto into which the straight end portion of the spring fits with a press fit, the washer contacting with the end of the resistor to which the spring is connected and being held between a first helical convolution of the spring and an end face of the resistor.

9. The resistor described in claim 4 characterized by the spring having a part of its helical extent imbedded in the resistor whereby some of the convolutions of the spring are dead within the material of the resistor but hold the spring firmly anchored to said resistor.

10. A carbonaceous resistor having a coil spring at one end thereof with convolutions of the spring spaced from one another and resisting movement toward one another to provide a compresison force for holding the resistor against a surface to which power is to be supplied, the spring having an end portion imbedded in the resistor, and the resistor being of one piece construction and formed around the imbedded portion of the spring whereby the spring is part of a unitary assembly with the resistor and can become disconnected from the resistor only by breaking the resistor.

11. The method of making a spring and resistor assembly which comprises placing a coil spring in a die cavity, with the convolutions of the spring spaced from one another, filling the portion of the die cavities that contains the spring with filler material that occupies the space within the spring including the space between the coils, leaving an end portion of the spring extending above the top level of the filler material, filling the die cavity above the filler material with a powdered carbonaceous material mix that surrounds the end portion of the spring, forming said powdered carbonaceous material mix into a solid resistor under pressure applied to the mix through the filler material at one end and by direct application of pressure to the powdered mix at the other end'thereof whereby the resistor is molded with the end portion of the spring imbedded therein.

12. The method described in claim 11 characterized by filling the die cavity with substantially incompressible and unreactive granular material that constitutes the filler material, then inserting a plunger into the die cavity above the granular material, inverting the die cavity, loading the die cavity above the granular material with the carbonaceous material mix, inserting another plunger into the die cavity above the carbonaceous material mix, compressing the granular filler material and the carbonaceous material mix between the plungers to mold it into the solid resistor with the end of the spring imbedded therein, then ejecting the spring and resistor assembly from the die cavity so that the unreactive granular filler material will fall free of the spring.

13. The method described in claim 11 characterized by the carbonaceous material mix including powdered carbon which extends for a substantial depth above the spring and powdered graphite above the powdered carbon with binder mixed with both the carbon and the graphite, the forming of the carbonaceous material into a solid resistor being performed by subjecting the mixes to sufficient pressure to mold them into the solid one piece resistor with a graphite end remote from the spring to provide a hard surface for hearing contact with a movable conductor.

V 14. The method described in claim 13 characterized by placinga mixture of powdered graphite and binder in the die cavity around the end portion of the spring, the powdered carbon mix and the other powdered graphite mix being placed on top of the powdered graphite and binder that is placed around the end portion of the spring.

15. The method described in claim 11 characterized by placing a washer over an end portion of the spring with a force fit, the die cavitybeing cylindrical and of substantially the same diameter as the washer and the end portion of the spring extending through the washer and beyond the washer on the side remote from the remainder of the spring, the filler material being kept from surrounding the end portion of the spring by said washer, then inverting the die cavity and adding the powdered carbonaceous mix to the die cavity above the washer and in contact with the washer.

16. The method of molding a resistor with a helical, open coil spring, having one end imbedded in the molded resistor, which method comprises inserting the spring and a powdered resistor mix in a die cavity and between plungers, applying force to urge the plungers together to compress the material between them, preventing con1- pression of the spring by placing a filler along most of the length of the spring in position to transmit force from one plunger to the powdered resistor mix, and compressing and molding the resistor mix around the part of the spring that is beyond the filler.

17. The method of making a resistor with a spring molded thereto and having its convolutions of a combined helical and spiral relation, which method comprises placing a washer'on an end portion of the spring and putting the spring and washer in a die cavity with the washer forming a partition across the die cavity, placing powdered mix for a resistor in the die cavity above the washer, compressing the mix with a plunger in the die cavity above the mix and with another plunger below the spring, bringing the plungers together to compress the mix and to deform the spring to a substantially flat spiral, and with pressure sufficient to set the mix and to form a rigid molded resistor with an end portion of the spring embedded therein, and thereafter rejecting the molded resistor from the die cavity whereby the spring expands to its original length.

18. As an article of manufacture, a permanently connected helical spring and electrical brush, which brush for its major portion having a molded body composed essentially of a powder mix of conducting material of high specific resistance, a filler, and a binder, and at least one terminal which is integrally secured to the brush body and in which one end of the helical spring is ern bedded, said terminal being formed in situ and consisting essentially of powder of substantially greater electrical 19. As an article of manufacture, a permanently connected coil spring and electrical brush, said spring having one end embedded in said brush, which brush for its major portion is formed of a carbon composition mix of powder, the end portion of said brush in which the spring is embedded being formed of a second powder of substantially greater electrical conductivity than the first named mix, said permanent connection, in the making of the brush, being efiected by integrally molding at least said mix and said second powder at the end of the brush all at the same time and with the end of the coil spring in situ within the second powder at the time of molding.

20. An article of manufacture comprising a molded carbonaceous resistor having a spring with an axially extending end portion permanently embedded in the carbonaceous resistor and having successive convolutions with a combined'helical and spiral relation, the convolution furthest from the resistor having the largest diameter and the convolutions being correlated so that they compress into'a flat spiral in a single plane.

21. An article of manufacture comprising a molded carbonaceous resistor having a graphite end portion merging into a body portion formed of a carbon powder mix and with a copper powder mix at the end remote from the graphite and permanently bonded to the carbon powder mix, a spring at the end of the resistor remote from the graphite, said spring having an end portion extending into and permanently connected with the end of the molded resistor having the powdered copper.

References Cited in the file of this patent UNITED STATES PATENTS 2,396,970 Riling Mar. 19, 1946 2,457,525 Brian Dec. 28, 1948 2,615,939 Mitchell Oct. 28, 1952 FOREIGN PATENTS 931,634 France Nov. 3, 1947 

1. IN AN IGNITION SYSTEM OF THE TYPE WHEREIN A DISTRIBUTOR HAS A ROTOR WITH A CONTACT EXTENDING FROM A CENTER PORTION OF THE ROTOR TO A MOVABLE CONTACT THAT IS MOVED BY THE ROTOR ACROSS A PLURALITY OF FIXED AND ANGULARLY SPACED CONTACTS CONNECTED WITH CONDUCTORS EXTENDING TO THE SPARK PLUGS OF THE IGNITION SYSTEM, AND IN WHICH POWER IS APPLIED TO THE ROTOR THROUGH A MAIN HIGH POTENTIAL LEAD ABOVE A CENTER REGION OF THE ROTOR, THE COMBINATION WITH SAID ROTOR OF A METAL HOLDER CONNECTED WITH THE HIGH POTENTIAL LEAD AND HAVING A SOCKET THEREIN IMMEDIATELY ABOVE THE ROTOR, A BRUSH THAT FITS INTO THE SOCKET AS A GUIDE AND THAT IS LONGITUDINALLY MOVABLE IN THE SOCKET, THE BRUSH HAVING AN END PORTION OF HARD GRAPHITE EXTENDING FROM THE SOCKET INTO CONTACT WITH THE CONTACT ON THE ROTOR, A SPRING IMBEDDED IN THE END OF THE BRUSH AND COMPRESSED BETWEEN THE INNER END OF THE BRUSH 